Apparatus for manufacture of cellulose esters



Feb. 5, 1935. U A T 1,990,113

APPARATUS FQR MANUFACTURE OF CELLULOSE E STERS Original Filed April 30,1929 2 Sheets-Sheet 1 Feb. 5, 1935. M, BURGHART 1,990,113

APPARATUS FOR MANUFACTURE OF CELLULOSE ESTERS Original Filed April 30,1929 2 Sheets-Sheet 2 l l l i I l l I l l Z A'ITOENEY Patented Feb. 5,1935 UNITED I STATE-s APPARATUS FOR MANUFACTURE OF CELLULOSE ESTERSLloyd M. Burghart, Linthicum Heights, Md., as-

signor to U. S. Industrial Alcohol 00., New York, N. Y., a corporationof West Virginia Original application April 30, 1929, Serial No.359,367, now Patent No. 1,839,295. Divided and this application June 25,1931, Serial No. 546,769

2 Claims.

This invention relates to apparatus for the manufacture of celluloseesters of organic acids, for example cellulose acetate, and forobtaining the same in "a physical condition favorable for drying and allother subsequent treatments In my PatentNo. 1,816,564, dated July 28,1931, I disclosed a process for making cellulose acetate, in whichliquid sulfur dioxid is employed to advantage as the reaction medium orsolvent. In the said patent and in Patent 1,822,563, dated September 8,1931, a continuation in part of Patent 1,816,564, I disclosed thatliquidsulfur dioxid was not only an advantageous liquid medium for theesterification reaction, but also for a thenensuing hydration treatment,the purpose of such treatment, as is well; known, being to convertsocalled primary cellulose acetate into an acetonesoluble form, or otherform more suitable for in dustrial purposes because of its solubilitycharacteristics. e I

The present application is a division of my Patent 1,839,295, datedJanuary 5, 1932,-a1so a continuation in part of Patent 1,816,564.

Patent 1,839,295 is directed to the process of making or obtainingcellulose esters of organic acids as a product of low apparent densityand loose structure, this being accomplished by dis charging thesolutions or fluid reaction masses from the pressure system under suchconditions that gaseous sulfur dioxid is abruptly released from theissuing material and is utilized to expand or disrupt the celluloseester. Precipitation of the cellulose ester is effected with the aid ofa sufiiciently large quantity of water or other liquid in which thecellulose esterisinsoluble and by which it is coagulated. By releasing.the gas from within the precipitating ester while it is in the act ofcoagulating in contact with the precipitating liquid an especiallyadvantageous result is secured. The opening up of the precipitatingmasses facilitates removal of unused acetic acid values and othersubstances which may bepresent. Furthermore, the physical condition ofthe ester is such that bleaching, p'urification, stabilizing and othersubsequent operations involving the penetration of treating agents aremade mucheasier. Also, the loose structure makes possible quick and easydrying, and is an advantage when it comes to dissolving the finishedproducts in various solvents prior to use. Cellulose acetate productsthus obtained, whether of the chloroform-soluble,alcohol-chloroform-soluble, oracetone-soluble type, or other type ofsolubility, may vary in the degree of subdivision, butgenerally'speaking are loose, fluffy and of low apparent density. Asidefrom the physical form, it is evident that the material is'much affectedin its structure by the expanding force.

The object of the invention claimed in the present application is toprovide apparatus for carrying out the process and producing the prodnotclaimed in Patent 1,839,295.

The apparatus includes a closed pressure vessel for holding thecolloidal solution or reaction mass under thevapor pressure of theliquid sulfur dioxid. This vesselis provided with an outlet for thefluid mass, from which outlet there extends a pipe provided with one ormore valves which can be opened to discharge the solution under thepressure of the sulfur dioxid. From this pipe the material is expelledinto an enclosed precipitation and gas-release chamber having an offtakethrough which the sulfur dioxid gas passes freely to a recovery system.Provision is made for causing the issuing solution to come into contactwith u the precipitating liquid in or adjacent this chambersimultaneously with the violent liberation of the gas. The interior ofthe chamber is at atmospheric pressure, or at very much lower pressurethan the high pressure under which the solution is discharged from thepressure vessel. Provision is also made for supplying heat at the regionof expansion and precipitation to overcome chilling efifect of thevaporization of-the sulfur dioxid and to insure instantaneousliberationof the gas in large volume.

.- In the accompanying drawings forming part Fig, 1 is a view partly inelevation and partly in section of one form of equipment for making thecellulose ester and for precipitating it in accordance with thisinvention; and

Fig. 2 is a similar view of another combination of equipment forcarrying out the invention.

In Fig. 1, the numeral 3 designates a closed reaction vessel adapted toretain the required pressure, this vessel being provided with a cover 4which can be tightly closed and can be removed, and with valved inlets 5and 20 for introducing liquid materials. Within the vessel there is astirrer 6 arranged to be driven by power. A discharge pipe 7 isconnected with the lower portion of the vessel and is provided Withoneor more valves 8. This pipe terminates in a nozzle 9 having a suitablenumber of comparatively small exit'openings, and when the charge, isprecipitated this nozzle is below the level of a body of water or otherprecipitating liquid in a chamber 10. This chamber is enclosed and hasan offtake .11 for collecting and freely conducting away the liquid, andwith a tight hinged bottom 13 for discharging the precipitatedcellulose, after the liquid has been drawn oii through a filter l4 and avalved line 15 leading to an acetic acid recovery system. A moderateamount of heat may. be supplied by a steam coil 16 in the bottom 13beneath the filter 14, or by a valvedsteam line 17'" having its outlet ashort distance above the filter 14 so as to be submerged by thebo'dy ofprecipitating liquid.

The material treated for esterificatio-n may be cellulose in anysuitable form, or a'=cellu1ose' derivative, for example,hydro-cellulose, and the acetylation may be preceded b'yanyappropriatepie-treatment.

The following is given as a specific example.

100 parts of cellulose, 260'parts of acetic anhydride as anacetylatingagent, 1000 parts of liquid sulfur dioxid, and 3 parts ofsulfuric-acid as a catalyst orcondensing agent, are digested and stirredin the vessel 3 at a suitable temperature, for example, at about 20-300., and at corresponding pressure, un'tiltest shows-that the reactionhas proceeded'to the d'esired degree.

The cellulose or cellulose derivative is placed in the vessel throughthe opening which is ordinarily tightly closed by the cover 4, and theliquid materials may be introduced through the valved inlet 5.

During the course of the treatment the cellulose loses its originalstructure and the cellulose acetate dissolves in the liquid sulfurdioxid, the result at the end of the operation being that of a thiclzishliquid or semi-fluid mass, practically homogeneous and readily flowablethrough pipes under pressure of the S02 gas or vapor; the preciseconsistency of the fluid mass or liquid varying according to the amountof liquid medium present and other conditions.

In the example given, it will be understood that the solution ofcellulose acetate in liquid sulfur dioxid existing when theacetylationreaction has been carried to the desired point, contains alsothe small amount of catalyst, the'surplus acetic anhydride and someacetic acid;

If cellulose acetate of a type resulting'from an acetylation reaction isdesired, or if the acetylation operation is not to be followed by ahydration treatment in the same general solution, the valve or valves 8are now opened, ahd'the fluid mass is delivered by the pressure-of theS02 through the pipe 7 and its perforated nozzle 9 into contact with thewater in the'chamber 10'; Bythe abrupt release of the gas pressure fromthe issuing streams the chloroform-soluble or alcohol-chloroform-solublecellulose acetate is disrupted atthe moment of precipitation, in themanner which has been described.

The employment of precipitating liquids other than water is permissibleand presents certain advantages. For example, in order to avoid thebreaking down of the surplus acetic anhydride, which is expensive, andto facilitate recovery of the acetic acid, the solution obtained at thistime can be precipitated in similar manner in'or with carbontetrachlorid, benzene; toluene" or other non-aqueous precipitatingliquid, to secure the light structured ester product.

The precipitated cellulose acetate, after preliminary separation fromthe liquid, may be washed and dried; and may then-constitute an articleof commerce; or, after washing or drying, or without performing theseoperations, it can be re-dissolved in liquid sulfur dioxid and then besubjected to a separate hydration treatment to modify it tel-anothertype of solubility.

For various reasons, however, it is advantageous, when theacetone-soluble variety, or some other variety, is desired, to proceedwith the hydration treatmentwithout separating the ester from theoriginal S02 solution or mixture resulting "from the acetylation stage.

This maybe carried out in the same vessel, but for operating economy itis more desirable to transfer the fluid reaction mass from theacetylation vessel to another closed pressure vessel 18, showzrirrl 'ig:2, the two vessels being connected byawalv'ed pipe 19 throughwhichthetransfer is made when the valve or valves are opened;

The-hydration treatment is essentially'a'diges tionof the solution ormixture, to which has been added a limited amount of a hydrating medium,typically'water, the amount of such water being less'than will causeprecipitation. As is well understood, the amount of hydrating agentshould bfe enoughtdbreak down the unused acetic an- The hydrating agentor mixture may be introduced'into the vessel 18,- but' there is apractical advantage in' admitting it to the mass in'the vessel 3 shortlybefore the'transfer of the contents tdtheyesself'l'il', advantage beingtaken of the thorough mixing action of the stirrer of the acetylating'vessel. 7

Asa concrete example, 55 parts of water and 6 parts of sulfuric acid mayb'e'introduced through the valved connection 20 to'the mixture in thevessel 3 about 20 minutes before the transfer is made, the mass beingthenrun into the vessel 18 and being there digested, preferably withmild stirring by-stirrers '21, until the test samples indicatethedesireddegree of acetonesolubility, or other desired type of solubility;This digestion may-'be'carried out at 6570 C., but lower tem-' peraturesaround 45 C. are preferable.

When the hydration treatment has-been carri'e'd asrar as is desired, thesolution is usually more liquid than that resulting from theacetylatio'n' reaction, and this? solution, consisting of celluloseacetate in solution or suspension; in the liquid sulfur dio'xid and"such amount of acetic acid asispresent, together with such' otheringredients as there maybe, is dischargedthrough the pipe 7 auditsnozzle 9, on the opening of the valve orvalves'll," into contact withwater orotlier precipitating liquid in an expansion chamber 10 "similarto the one already described;

It is sufiicien'tthatfthe pressure at' the precipitating and expandingregion be approximately atmospheric, thougli'natur'ally' the explosiveaction of the gas on the colloidal masses'm'ay be promoted by partialvacuum or by heat or by both.

The sudden andsubstantially complete release of the gas pressure fromwithin the precipitating r'r'rasses and'the' effect the form andstructure of the product is substa'iitially' the same as in the case ofprimary celluloseacetate.

The invention is also applicabletome-manufacture and treatment of othercellulose esters of organic acids, for example cellulose propionate andcellulose benzoate.

The products after being precipitated are washed and dried in a suitablemanner.

The invention is also applicable to the treatment of previouslymanufactured esters of cellulose, obtained by any process ofmanufacture. For example, cellulose acetate, of any of the types ofsolubility, which has been made by the usual process in an acetylatingbath consisting of acetic anhydride, acetic acid and sulfuric acid, andwhich has or has not been hydrolyzed, can, at any time, after thecompletion, or partial completion, of its manufacture, be put intosolution in liquid sulfur dioxid and be discharged from the region ofhigh pressure where it is so held into a region of low pressure where itis precipitated in contact with water or an equivalent medium, in orderto put the material into the improved physical condition the attainmentof which constitutes the ultimate object of the invention hereinclaimed.

As a further extension of the invention, the cellulose esters can bemade and/ or hydrated by any of the known processes, for example thoseutilizing glacial acetic acid as a liquid medium,

' and when the acetylation and/or the hydration has been carried to thedesired stage of comple-.

tion, or before such time, an amount of liquid sulfur dioxid sufficientto provide an enormous volume of gas can be introduced into' a closedpress sure vesselcontaining the reaction mixture, and the solution canthen be discharged and precipitated in the manner described so as toeiiect the opening up of the ester masses.

' In each of the applications of the invention which have been describeda solution, or a condition similar to a solution, of the desiredcellulose.

pressure, and it seems likely that the collapse of such films and thefurther setting of the cellulose ester structure accounts for the kindof gross structure which may be obtained.

I claim:

1. Apparatus for obtaining cellulose esters in disrupted condition fromcolloidal solutions, comprising a closed vessel adapted to hold thesolution under the pressure of a normally gaseous constituent, aprecipitation and gas-release enclosure, means for conducting gas fromsaid enclosure for recovery and for insuring a relatively low pressurein said enclosure, a conduit constituting a direct connection betweenthe lower portion of said vessel and said enclosure adapted to transferthe entire charge from the former to the latter, valve means for closingsaid conduit, and for opening the same so that the solution will bedischarged under pressure from said vessel and released from pressure insaid enclosure, a perforated outlet for delivering the solution in theform of jets, and means for supplying a precipitating liquid to contactwith the issuing jets, substantially as and for the purpose set forth.

2. Apparatus for obtaining cellulose esters in disrupted condition fromcolloidal solutions, comprising a closed vessel adapted to hold thesolution under the pressure of a normally gaseous constituent, aprecipitation and gas-release enclosure, means for conducting gas fromsaid enclosure for recovery and for insuring a relatively low pressurein said enclosure, aconduit constituting a direct connection between thelower portion of said vessel and said enclosure adapted to transfer theentire charge from the former to the latter, valve means for closingsaid conduit, and for opening the same so that the solution will bedischarged under pressure from said vessel and released from pressure insaid enclosure, a perforated outlet for delivering the solution in theform of jets, means for supplying a precipitating liquid to contact withthe issuing jets, and means for supplying heat to the issuing solutionand the precipitating liquid, substantially as and for the purpose setforth.

LLOYD M. BURGHART.

